Cracking processes historically have been utilized in oil refineries and petrochemical plants to convert heavy hydrocarbon streams into lighter hydrocarbon fractions. Although the field of oil- and petrochemical refinement is referred to as one of the well-established and deep-rooted technological areas, one of the trends, emerging in oil- and petrochemical industry, requires that any developing technology would meet two major requirements. Those requirements may be briefly formulated as energy saving and reducing consumption of feedstock extracted from the non-renewable sources of raw materials. Those are also issues to consider for the development of one of the main petrochemical processes—large-scale production of lower (low molecular weight) olefins.
Low-molecular olefins, such as ethylene, propylene and butylenes, are the basic products of petrochemical industry and serve as a feedstock in commercial production of plastics, rubbers, polymers, elastomers and other synthetic materials, as well as of fibres and coatings. The existing production technology for lower olefins, comprising pyrolysis of medium weight hydrocarbons, such as naphtha or gasoil and light hydrocarbons like pentanes, butanes, propane and ethane, down to lightweight substantially unsaturated polymerizable components in the tubular furnace, was created more than half a century ago and hardly satisfies modern requirements of cost-effective feedstock utilization. Tubular furnaces have restrictions for the pyrolysis process: reaction temperature cannot be increased because tube material durability as well as heat transfer from tube walls to process gas has physical limits. This leads to feedstock residence time, which is not optimal for the process. Insufficient feedstock heating rate in tubular cracking furnaces lead to increased duration of pyrolysis process. This fact results in situation, when formed at initial stages olefins reside in the reactor furnace for sufficiently long time to begin entering into secondary reactions, natural consequence of which is a loss of a target product. Secondary product also includes coke, which causes heat transfer problems in tubes and fouling in equipment located downstream. Traditional technology does not offer a reasonable solution for eliminating of aforesaid problem, since heat transfer rates in radiant sections of conventional pyrolysis furnaces have already reached technical limits. In conventional tubular reactors heat is thus delivered to the reaction zone through the reactor walls.
Other than tubular furnaces solutions for pyrolysis equipment are known. Those include rotary reactors with complicated rotor blade arrangement. Costs for building and maintaining such equipment are higher than the profits that could be ever obtained by means thereof.
Traditional process for producing low-molecular weight hydrocarbons by thermal degradation thus encounters the following problems: 1. poor performance factor for tubular furnace reactors; 2. loss of valuable feedstock material; 3. long reaction times; 4. high secondary reactions rates; 4. high energy consumption; 5. non-optimum (less than possible) product yield and selectivity.